1. Technical Field
The present invention relates to an optical fiber adapter, and more particularly, to a one-piece optical fiber adapter.
2. Description of the Related Art
Optical fiber connectors are an essential part of substantially all optical fiber communication systems. For instance, such connectors are used to join segments of fiber into longer lengths, to connect fiber to active devices such as radiation sources, detectors and repeaters, and to connect fiber to passive devices such as switches and attenuators. The principal function of optical fiber connectors is to hold an optical fiber such that its core is axially aligned with the optical path of the device to which the connector is mating. This way the light from one fiber is optically coupled to the optical path of the mating device.
Reference is made to FIGS. 1a and 1b, which respectively illustrate conventional multi-fiber MPO male and female type connectors 110a, 110b. Each of the optical fiber connectors 100a and 100b has a rectangular key protrusion 112 formed on the upper surface of the front section thereof. Located on two opposing lateral surfaces of the front section are two indentations 114. A plurality of optical fibers 130 are exposed from and flush with the front end surface 120 of the front section. Two guide pins 140 protrude from the end surface 120 of the optical fiber connector 100a while two guide holes 150 are formed on the end surface 120 of the optical fiber connector 100b to respectively receive the guide pins 140 of the connector 100a. 
In order to couple the optical fiber connectors 100a and 100b with each other, it needs to use a corresponding optical fiber adapter. Reference is made to FIG. 2, which illustrates a conventional MPO type optical fiber adapter 200. The optical fiber adapter 200 has a hollow main body with two opposing openings 210 in an axial direction into which the connectors 100a and 100b may be respectively inserted. To firmly mate with the connectors 100a and 100b, two pairs of hooks 220 are positioned to respectively extend out from the openings 210 of the adapter 20. In addition, two rectangular indentations 230 are formed on the inner walls of the adapter 20 respectively near the openings 210 to receive the key protrusions 112 of the connectors 100a and 100b. 
When the connectors 100a and 100b are respectively inserted into the adapter 200 through the openings 210 to couple with each other, the hooks 220 will respectively hook on to the connectors 100a, 100b at the indentations 114. The guide pins 140 of the connector 100a are respectively inserted into the guide holes 150 of the connector 100b and the optical fibers 130 exposed out from the connectors 100a and 100b are brought into contact with each other accordingly. This way the light from one fiber may be optically coupled to the coupled fiber.
The function of the indentations 230 is to receive the key protrusions 112 at the connectors 100a, 100b such that the connectors 100a, 100b may be inserted into the adapter 200 with only predetermined orientations. As illustrated in FIG. 2, when the connector 100a or 100b of FIGS. 1a, 1b is positioned with its key protrusion 112 being oriented up, it cannot be inserted into the adapter 200 through the openings 210. When the connector 100a or 100b is turned over such that the key protrusion 112 is oriented down, it may be inserted into the adapter 200. Therefore, the orientations of the indentations 230 limit the coupling of the connectors 100a and 100b to the predetermined polarity.
However, it is necessary to change the coupling polarity of the connectors for some applications. It means that the indentation 230 of the adapter 200 is positioned up such that the connector 100a or 100b may be inserted into the adapter 200 with its key protrusion 112 being oriented up.